真口 宏介, 小山内 学, 潟沼 朗生, 高橋 邦幸

Hiroyuki MAGUCHI, Manabu OSANAI, Akio KATANUMA, Kuniyuki TAKAHASHI

手稲渓仁会病院消化器病センター

Center for Gastroenterology, Teine-Keijinkai Hospital

キーワード : pancreatic neoplasm, cystic neoplasm of the pancreas, ultrasonography, endoscopic ultrasonography, intraductal ultrasonography

臨床の場で遭遇する膵腫瘍の診断名の数は限られ，各腫瘍の病理と画像所見の特徴を把握しておくことで鑑別診断の多くが可能となる．膵腫瘍は大きく充実性と嚢胞性に分けられる．充実性には，通常型膵癌，内分泌腫瘍，Solid-pseudopapillary neoplasm（SPN），特殊型膵癌（腺扁平上皮癌，退形成性癌など），腺房細胞癌があり，嚢胞性では，漿液性嚢胞腫瘍（serous cystic neoplasm: SCN），粘液性嚢胞腫瘍（mucinous cystic neoplasm: MCN），膵管内乳頭粘液性腫瘍（intraductal papillary mucinous neoplasm: IPMN）の鑑別を行うことになる．但し，充実性腫瘍の嚢胞化あるいは充実性腫瘍の周囲に貯留嚢胞や仮性嚢胞を形成する場合には充実と嚢胞の混在する病態を呈するため鑑別診断に際し注意する必要がある．充実性腫瘍の鑑別診断で問題となるのは，特殊型膵癌（腺扁平上皮癌，退形成性癌など）と腺房細胞癌，非典型的所見を呈する内分泌腫瘍である．特に，内分泌腫瘍は内部の嚢胞化や主膵管内腫瘍栓など，種々の所見を呈するため注意を要する．嚢胞性腫瘍では，SCNにおいてmicro cystとmacro cystの混在，あるいはmacro cyst主体の例が少なくないことを認識しておく必要がある．MCNとIPMNでは，共通の被膜の有無，嚢胞の構造が内に向かうか外に向かうかが鑑別ポイントとなる．膵腫瘍の鑑別診断において体外式US，EUS，IDUSなど超音波診断の果す役割は大きい．

Although relatively few types of pancreatic neoplasms are normally encountered in the clinic, understanding their ultrasonographic findings based on histopathology is important in their differential diagnosis. Pancreatic neoplasms are generally classified as solid or cystic. The solid neoplasms include pancreatic carcinoma, endocrine tumor, Solid-pseudopapillary neoplasm (SPN), adenosquamous carcinoma, anaplastic carcinoma, and acinar cell carcinoma; cystic neoplasms, serous cystic neoplasm (SCN), mucinous cystic neoplasm) (MCN), and intraductal papillary mucinous neoplasm (IPMN). However, differential diagnosis must be carefully carried out when the tumor is solid and presents such cystic features as a solid neoplasm with cystic degeneration with a retention cyst or a pseudocyst. With solid neoplasms, it is sometimes difficult to distinguish among adenosquamous carcinoma, anaplastic carcinoma, acinar cell carcinoma, and endocrine tumor with atypical features. Endocrine tumors in particular often show diverse features resulting from cystic degeneration or tumor thrombus in the main pancreatic duct. With cystic neoplasms, it is important to acknowledge that SCN often consists of both micro and macro cysts, or mainly macro cysts. It is also important to recognize the cyst-in-cyst structure of MCN and the cyst-by-cyst structure of IPMN. Ultrasonographic examinations play a critical role in the differential diagnosis of pancreatic neoplasms.